Detecting OpenGL errors has been a common problem, since OpenGL does not give you error messages unless you ask for them. Even if you don't have any visual problems in your code, resolving OpenGL errors is still important, because most OpenGL implementations generate error codes without waiting for you to ask for them, and this may affect the performance of your code. This solution provides a simple way to retrieve OpenGL error strings that help you locate the problem.

OpenGL errors can be retrieved using glGetError function, which returns a GLenum value that can be converted to a string using gluErrorString function as follows:

GLenum error = glGetError();
cout << gluErrorString( error );

For keeping things simple I prefer to use the following macro:

#define CHECK_OPENGL_ERROR \
{ GLenum error; \
  while ( (error = glGetError()) != GL_NO_ERROR) { \
    printf( "OpenGL ERROR: %s\nCHECK POINT: %s (line %d)\n", \
      gluErrorString(error), __FILE__, __LINE__ ); \
  } \
}

Simply copy and paste it into one of your source files, preferably a header file that all other OpenGL related source files include. Then place CHECK_OPENGL_ERROR before and after suspicious OpenGL calls. For example, the following code calls glTranslatef between glBegin and glEnd, which is invalid. To detect this error, we place two CHECK_OPENGL_ERROR lines as follows:

CHECK_OPENGL_ERROR
glBegin( GL_POINTS );
glVertex3f( 1.0f, 0.0f, 0.0f );
glTranslatef( 2.0f, 2.0f, 2.0f );
glVertex3f( 1.0f, 0.0f, 0.0f );
glEnd();
CHECK_OPENGL_ERROR

When you execute this code, it prints "invalid operation" with the source file name and the line number where the second CHECK_OPENGL_ERROR is placed. Note that, CHECK_OPENGL_ERROR only prints the errors that occurred before the macro. Therefore, to be able to locate the error we need to use two CHECK_OPENGL_ERROR macros as shown above. If the first one does not generate an error message, we can be sure that the error happens between the two CHECK_OPENGL_ERROR macros.

Once you make sure that your code does not have OpenGL errors, you may want to disable the error checking. One way to do it is, of course, deleting all the CHECK_OPENGL_ERROR lines. However, you may want to enable them later, after you make couple more changes in the code. Here I will offer another simple way to disable the error checking without actually removing CHECK_OPENGL_ERROR lines:

//#define DISABLE_CHECK_OPENGL_ERROR
#ifndef DISABLE_CHECK_OPENGL_ERROR
 #define CHECK_OPENGL_ERROR \
 { GLenum error; \
   while ( (error = glGetError()) != GL_NO_ERROR) { \
     printf( "OpenGL ERROR: %s\nCHECK POINT: %s (line %d)\n", \
       gluErrorString(error), __FILE__, __LINE__ ); \
   } \
 }
#else
 #define CHECK_OPENGL_ERROR
#endif

Here, just by uncommenting the first line you can disable all OpenGL error checking.